Many analytical techniques and systems are based upon the ability of various materials to form a specific binding pair. As used herein, a specific binding pair is a system wherein the two components share an affinity for each other so as to cause one of the components contained in a mixture of materials to bind to the other upon contact. Either or both components of a specific binding pair may be organic or inorganic. Some examples of specific binding pairs are antibodies and antigens, nucleic materials such as DNA, RNA and fragments thereof, free nucleotides, metallic moieties and nucleic acids or proteins, metal ions-organic ligands, biotin and avidin, folic acid-folate binding protein, polysaccharides-polysaccharide binding protein, sulfhydryls and sulfhydryl reactive groups such as maleimides and haloacetyl derivatives, amines and amine reactive groups such as succinimidyl esters and isothiocyanates, etc.
Typical assays based upon the formation of specific binding pairs include a reporter system which provides a detectable signal indicative of the formation of a specific binding pair. For example, one of the members of the pair can be provided with a label which can comprise a fluorescent material, a radioactive material, any other signaling moiety, or a material which is further reactive with another species to form a colored complex or some other such detectable reaction product. The reporter system in these types of assays is commonly referred to as a layered-type system wherein successive layers of reagents such as labeled antibodies or nucleic acid probes are applied one after another in successive manipulation to generate a detectable signal.
Recently, a number of technologies have been developed which enable the production of very large arrays comprised of one or more differing materials such as oligonucleotides, DNA and/or RNA and/or fragments thereof, peptides, protein fragments, cell fragments, cells and tissues disposed upon a support body. The various members comprising the array are each capable of forming a unique, specific binding pair with their appropriate counterpart, and such arrays have great utility for rapidly screening mixtures for the presence or absence of a large number of materials. Techniques for the fabrication of such arrays will be found, for example, in U.S. Pat. Nos. 5,744,305; 5,489,678; 5,445,934; 5,405,783; 5,329,028; 5,143,854 and 4,419,444, the disclosures of which are incorporated herein by reference. The formation of specific binding pairs is detected in such arrays by utilizing conventional reporter technology, of the type described hereinabove.
There is often a need to increase the sensitivity of such assays. For example, in many instances, species will be present in the mixture at very low concentrations; hence, the detectable signal produced thereby will be very weak. Target amplification techniques, such as polymerase chain reaction (PCR) amplification may be applied to a sample containing nucleic materials so as to increase the concentration of these materials. However, PCR reaction, can be time consuming and difficult to implement. Therefore, it will be appreciated that there is a need for an array-based analytical system and method having an enhanced sensitivity which does not require such complex sample preparation or manipulation. The enhanced sensitivity of an assay of this type would allow for rapid and simple analysis of relatively unmodified biological fluids, preparations and the like. As will be described in detail hereinbelow, the present invention incorporates an amplification system into an array-based analysis. The system of the present invention may be utilized for the analysis of materials such as oligonucleotides, DNA and/or RNA and/or fragments thereof, peptides, protein fragments, polysaccharides, cell fragments, cells and tissues.